どんなエラー？

こんな具合に例外を投げます。

$ ./script/rails server
/usr/lib/ruby/gems/1.8/gems/execjs-1.2.7/lib/execjs/runtimes.rb:47:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
from /usr/lib/ruby/gems/1.8/gems/execjs-1.2.7/lib/execjs.rb:5
from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee_script.rb:1
from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
from /usr/lib/ruby/gems/1.8/gems/coffee-script-2.2.0/lib/coffee-script.rb:1
from /usr/lib/ruby/gems/1.8/gems/coffee-rails-3.1.1/lib/coffee-rails.rb:1:in `require'
from /usr/lib/ruby/gems/1.8/gems/coffee-rails-3.1.1/lib/coffee-rails.rb:1
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:68:in `require'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:68:in `require'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:66:in `each'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:66:in `require'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:55:in `each'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler/runtime.rb:55:in `require'
from /usr/lib/ruby/gems/1.8/gems/bundler-1.0.18/lib/bundler.rb:120:in `require'
from /home/shingo/Aptana RadRails Workspace/twitter_bot/config/application.rb:7
from /usr/lib/ruby/gems/1.8/gems/railties-3.1.0/lib/rails/commands.rb:52:in `require'
from /usr/lib/ruby/gems/1.8/gems/railties-3.1.0/lib/rails/commands.rb:52
from /usr/lib/ruby/gems/1.8/gems/railties-3.1.0/lib/rails/commands.rb:49:in `tap'
from /usr/lib/ruby/gems/1.8/gems/railties-3.1.0/lib/rails/commands.rb:49
from ./script/rails:6:in `require'
from ./script/rails:6
$